1. Field of the Invention
The present invention relates to facilitating the operation of hinged access doors, and particularly to enhancing the ease of use of the manual operator of a door mounted, spring loaded, latch bolt. More specifically this invention is directed to apparatus for converting conventional locksets having knob-type operators to locksets having lever-type operators, and especially to apparatus which allows such a conversion without replacement of the existing cylinder lock. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
Key-in-knob locks, also commonly called cylindrical locks, are well known in the art. Because of their ease of installation, and also because many such lock assemblies have the capability of being "rekeyed", key-in-knob locks have been widely employed in public and commercial buildings on doors which control access to areas which do not require a high degree of security. An example of a typical prior art key-in-knob lockset may be seen from U.S. Pat. No. 2,355,682.
Knob-type latch bolt operators have the disadvantage of being difficult to manipulate by many disabled persons. The Americans with Disabilities Act (ADA), which was passed in 1990, requires that most knob-type operators in buildings which are accessible to the public be changed so as to employ easier-to-use lever type operators. The necessity of a change-over from a knob to a lever presents several possibilities. The first possibility, which carries a significant economic penalty as well as substantial inconvenience, requires removal of the existing key-in-knob lockset in its entirety and installation of a new lockset having a lever-type operator. In other words, a servicable and comparatively expensive cylindrical lock, and possibly also the associated latch bolt, is replaced in the interest of changing only the manual operator of the lockset. Such replacement obviously entails the incurrence of significant labor and hardware costs.
A second possibility is to retrofit the knob of the existing lockset with a lever handle. This possibility, in the past, has not proven to be a practical solution. The retrofit kits which have been available have consisted of plastic parts which were secured over the hub or shank of the existing lock and thus, in effect, bolted to the knob. In order to prevent sagging, the lever handles of such kits were light weight and thus lacking in durability. In practice, breakage of such plastic handles has been a significant problem.
A third approach, which has not achieved commercial success, is to modify the existing lockset using a conversion kit. The conversion kits which have been proposed have been exceptionally complex, and the conversion hardware was thus expensive, and installation thereof was highly labor intensive. Accordingly, any possible cost savings vis-a-vis total lockset replacement have been minimal.
A lever-type latch bolt operator, as a result of lever action, inherently imposes a higher torque load on an associated cylindrical lock than does a knob-type operator. Many conventional prior-art key-in-knob locksets are not constructed so as to have sufficient strenth to withstand the additional stress which would be imposed by a lever-type operator acting directly on the shell housing of the lock cylinder. Also, the key plugs of most key-in- knob locksets are arranged with the keyway oriented vertically while lever sets customarily have their keyways horizontally oriented. This difference in keyway orientation presents a further difficulty in conversion.